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s390/uaccess: get_user() should zero on failure (again)

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Commit fd2d2b191f ("s390: get_user() should zero on failure")
intended to fix s390's get_user() implementation which did not zero
the target operand if the read from user space faulted. Unfortunately
the patch has no effect: the corresponding inline assembly specifies
that the operand is only written to ("=") and the previous value is
discarded.

Therefore the compiler is free to and actually does omit the zero
initialization.

To fix this simply change the contraint modifier to "+", so the
compiler cannot omit the initialization anymore.

Fixes: c9ca78415a ("s390/uaccess: provide inline variants of get_user/put_user")
Fixes: fd2d2b191f ("s390: get_user() should zero on failure")
Cc: [email protected]
Cc: Al Viro <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
This commit is contained in:
Heiko Carstens 2017-03-27 09:48:04 +02:00 • committed by Martin Schwidefsky
commit d09c5373e8
1 changed files with 1 additions and 1 deletions
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2
arch/s390/include/asm/uaccess.h
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@ -147,7 +147,7 @@ unsigned long __must_check __copy_to_user(void __user *to, const void *from,
" jg 2b\n" \
".popsection\n" \
EX_TABLE(0b,3b) EX_TABLE(1b,3b) \
: "=d" (__rc), "=Q" (*(to)) \
: "=d" (__rc), "+Q" (*(to)) \
: "d" (size), "Q" (*(from)), \
"d" (__reg0), "K" (-EFAULT) \
: "cc"); \